7 GRAND DAD is a bootleg NES title that is a reskin of the game The Flintstones: The Rescue of Dino and Hoppy that replaces Fred Flintstone's head with Mario's head. It became a wildly popular meme due to Vinesauce Joel's shocked reaction to its bizarre title screen, and is also an iconic fixture of SiIvaGunner's high-quality rips, as well as a character in the Weegee lore. The Mario seen on said title screen (itself a reskin of another bootleg Mario named Fortran), often just called Grand Dad.

More facts here: https://fridaynightfunking.fandom.com/wiki/Friday_Night_Funkin%27:_Mario%27s_Madness/Characters_(Overworld)#Grand_Dad